Experience has shown that the catastrophic failure of an integrated circuit chip, such as a microprocessor, will occur (if at all) during the initial phase of the chip life. If the chip passes its "infant mortality" phase, the life and reliability of the chip will have a relatively high probability.
To precipitate early chip failure, the chip is "exercised" or powered while being subjected to relatively high external temperatures. Typically, a batch of chips is electrically powered in an oven where the temperature is maintained at approximately 150.degree. C. for an extended period of time, such as 1,000 hours. This is referred to in the art as "burn-in".
During burn-in, a batch of chips may be mounted on a mother board, and the chip leads are electrically connected to respective circuit elements on the mother board by a suitable means, such as one or more flexible electrical connectors. Maintaining good electrical contact between the chip leads and the flexible electrical connector is very important. Where the leads are made of gold, the electrical contact is usually not a major problem; but where the chip leads are tin plated, a relatively high retention force is necessary to assure good electrical contact. This is due to oxidation of the tin-plated chip leads. Oxidation will occur in the interval between the tin-plating bath or process and the burn-in stage, an interval of perhaps a few weeks. Even if the oven has a nitrogen atmosphere, it is still necessary to maintain a relatively-high clamping force to retain the chip frames and assure good electrical contact with the chip leads.
In order to maintain the necessary retention force, especially where the chip leads are tin-plated, a system of levers or oversized latches are necessary in order to achieve the necessary mechanical advantage for the desired retention force. However, because of space problems, this is not feasible nor particularly desirable since it reduces the total number of chips on the board and thus reduces production rates.
For large batches of chips, the testing apparatus is fully automated and includes robotic arms for transferring the batches of chips into and out of the oven. In production, and because of the relatively large number of chips being burned-in, the prior clamping mechanisms interfere with the high-speed automated apparatus for transferring large batches of chips.